This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-336081, filed Nov. 26, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a catheter such as a vasolidation catheter for dilating a stenosis within the blood vessel for curing the stenosis so as to improve the blood flow on the side of the periphery of the stenosis and a method for manufacturing the particular catheter.
The advent of a microcatheter has made it possible to perform therapy and diagnosis within a fine blood vessel or vasalium, though the conventional catheter is said to be incapable of performing such a therapy and diagnosis. The microcatheter includes, for example, a percutaneous transluminal coronary angioplastry catheter, hereinafter referred to as a PCTA dilatation catheter, used for curing the myocardial infarction or angina pectris. The PTCA dilatation catheter includes in general an outer tube having an inflation lumen, an inner tube having a guide wire lumen, an inflatable member (balloon) bonded in the vicinity of the distal ends of the inner tube and the outer tube, and a hub mounted to the proximal end portion of the inner tube and the outer tube. As described above, the catheter tube constituting the PTCA dilatation catheter requires at least two lumens. Therefore, a biaxial plastic tube, i.e., a plastic tube having openings in its cross section such as a double lumen, or a plastic tube of a coaxial structure such as a coaxial catheter tube is generally used for the PTCA dilatation catheter.
The PTCA dilation catheter formed of the biaxial catheter tube has an advantage that satisfactory pushability can be obtained. However, the biaxial catheter tube is poor in operability of the guide wire and is not suitable for decreasing the diameter of the catheter tube.
Under the circumstances, a catheter tube of a coaxial structure is mainly used in recent years for forming the PTCA dilatation catheter. The technology for improving trackability and pushability for the catheter of the coaxial structure within the blood vessel is disclosed in, for example, U.S. Pat. No. 5,496,275 and U.S. Pat. No. 5,759,191.
The catheter disclosed in U.S. Pat. No. 5,496,275 is constructed such that an inner tube and an outer tube are bonded to each other over a considerable distance between a position considerably away from a balloon toward the proximal end of the outer tube and the proximal end of the balloon so as to form a narrowed passageway for balloon inflation fluid. In this construction, it is necessary for the balloon inflation fluid to pass through a narrow fluid passageway from a position considerably in front of the balloon. Therefore, flow of the inflation fluid required for inflating the balloon is obstructed, resulting in a poor response time to inflation and deflation of the balloon.
The catheter discloses in U.S. Pat. No. 5,759,191 is constructed such that an inner tube and an outer tube are bonded to each other within a balloon with an annular spacer, and that a small opening is formed through the wall of the outer tube. In this construction, the balloon inflation fluid passes through the small opening made in the wall of the outer tube in a direction perpendicular to the long axis of the shaft so as to be injected into and discharged from the balloon. Therefore, the balloon inflation fluid fails to flow smoothly, resulting in a poor response time to inflation and deflation of the balloon. An additional problem is that, since the inner tube and the outer tube are bonded to each other, a troublesome manufacturing step is required.
Further, Japanese Patent Disclosure No. 11-19216 discloses a method of easily bonding an inner tube and an outer tube constituting a catheter tube. In this method, the inner tube and the outer tube are formed of compatible materials, and the outer tube is irradiated with a light beam for thermal fusion bonding of the tubes. In the method disclosed in this prior art, a mandrel for retaining a first lumen is inserted into the inner tube, and a mandrel for retaining a second lumen is inserted into the clearance between the inner tube and the outer tube. Under this condition, the outer tube is irradiated with the light beam. The reason that the mandrel for retaining the second lumen is inserted into the clearance between the inner tube and the outer tube is to prevent the second lumen from being blocked by thermal deformation of the inner and outer tubes caused by heat transfer to regions other than the focused region of the light beam. Since it is necessary to insert the mandrel for retaining the second lumen into the clearance between the inner and outer tubes, a troublesome manufacturing step is required in this prior art. In addition, since the outer tube is thermally deformed by the irradiation with the light beam not only on the inner surface but also on the outer surface, the appearance of the catheter is impaired.
An object of the present invention is to provide a method for manufacturing a catheter, which permits easily bonding the inner tube and the outer tube to each other in a short time without using a mandrel for retaining a lumen between the inner tube and the outer tube.
Another object of the present invention is to provide a catheter being pushed favorably in the blood vessel, which is free from thermal deformation of the inner tube and the outer tube in regions other than the bonded portion, which is satisfactory in response time to inflation and deflation of the inflatable member because the interruption of the fluid passageway of the inflation fluid and the obstacle to the inflow of the inflation fluid into the inflatable member are negligibly small, and which is satisfactory in the appearance of the outer surface of the outer tube.
According to a first aspect of the present invention, there is provided a method for manufacturing a catheter comprising an inner tube forming a first lumen and an outer tube arranged coaxial with the inner tube, a second lumen being formed between the outer surface of the inner tube and the inner surface of the outer tube, comprising steps of: inserting a mandrel for retaining the first lumen into the inner tube; and applying an ultrasonic horn to the outer surface of the outer tube for oscillating ultrasonic waves, thereby fusion bonding the inner surface of the outer tube to the outer surface of the inner tube.
In the method of the present invention, the inner surface of the outer tube is fusion bonded to the outer surface of the inner tube by utilizing an ultrasonic oscillation. Therefore, the thermal deformation does not take place in portions other than the bonded portion. In addition, it is unnecessary to use a mandrel for retaining a second lumen between the inner tube and the outer tube during the bonding operation. Since it suffices to perform the fusion bonding operation utilizing an ultrasonic oscillation only with a mandrel for retaining the first lumen inserted into the inner tube as described above, the inner tube and the outer tube are bonded to each other easily and in a short time.
According to another aspect of the present invention, there is provided a catheter, comprising: an inner tube forming a first lumen and having an opening at a distal end; an outer tube arranged coaxially with the inner tube and having a distal end positioned at the proximal side to the distal end of the inner tube, a second lumen being formed between the outer surface of the inner tube and the inner surface of the outer tube; a deflated or folded inflatable member having a distal end portion secured to the inner tube and having a proximal end portion secured to the outer tube, and being in communication with the second lumen at the proximal end portion; a first port having an opening in communication with the first lumen; and a second port having an opening in communication with the second lumen; wherein a part of the inner surface of the outer tube is fusion bonded to a part of the outer surface of the inner tube by utilizing ultrasonic oscillation.
In the catheter of the present invention, only a region corresponding to at most 90% of the wall thickness of each of the outer tube and the inner tube from the bonding surface between the inner surface of the outer tube and the outer surface of the inner tube is thermally deformed. In other words, a region corresponding to at least 10% of the wall thickness of the outer tube from the outer surface of the outer tube and a region corresponding to at least 10% of the wall thickness of the inner tube from the inner surface of the inner tube are scarcely subjected to the thermal deformation. Also, those regions of the outer tube and the inner tube that are away from the bonded region are not subjected to the thermal deformation.
In the present invention, it is desirable for the bonded portion between the inner surface of the outer tube and the outer surface of the inner tube to be formed over a region corresponding to 5 to 95% of the outer circumferential surface of the inner tube and over a length of 0.3 to 30 mm in the axial direction.
In the catheter of the present invention, the inner tube and the outer tube are not thermally deformed in regions other than the bonded portion as described above. As a result, the interruption of the fluid passageway of the inflation fluid and the obstacle of the inflow of the inflation fluid into the inflatable member are very small, leading to a good response time to inflation and deflation of the inflatable member. In addition, appearance of the outer surface of the outer tube is kept favorable.
In the catheter of the present invention, the inner tube and the outer tube are fixed to each other at the bonded portion. Thus, the inner tube can be prevented from being bent, curved or twisted inside the outer tube. Therefore, a pushing force imparted to the proximal portion of the catheter is not absorbed by intermediate parts thereof but can be reliably transmitted to the distal end thereof. Thus, the pushability (trackability or travel performance in blood vessel) of the catheter in a blood vessel is preferable.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.